Re: [libvirt] [RFC] exporting KVM host power saving capabilities through libvirt

On Tue, Jun 28, 2011 at 08:55:31PM +0530, Vaidyanathan Srinivasan wrote: > Hi, > > Linux host systems running KVM support various power management > capabilities. Most of the features like DVFS and sleep states can be > independently exploited by the host system itself based on system > utilisation subject to policies set by the administrator. > > However, system-wide low power states like S3 and S4 would require > external communication and interaction with the systems management > stack in order to be used. The first steps in this direction would be > to allow systems management stack to discover host power saving > capabilities like S3 and S4 along with various other host CPU > capabilities. > > Libvirt seems to be the main glue layer between the platform and the > systems-management stack. Adding host power savings capabilities as > part of libvirt host discovery mechanism seems to be one possible > approach without addition of any new APIs or agents. > > libvirt has virConnectGetCapabilities() that would export an XML file > describing the capabilities of the host platform and guest features. > > KVM hypervisor's capability to support S3 can be exported as a host > feature in the XML as follows: > > <host> > <uuid>94a3492f-2635-2491-8c87-8de976fad119</uuid> > <cpu> > <arch>x86_64</arch> > <features> <<<=== New host feature fields > <S3/> > <S4/> > </features> > <model>Westmere</model> > <vendor>Intel</vendor> > <topology sockets='1' cores='2' threads='2'/> > <feature name='rdtscp'/> > <feature name='xtpr'/> > <feature name='tm2'/> > <feature name='est'/> > <feature name='vmx'/> <<<= These are host CPU features > > System management software that works through libvirt, already queries > this capabilities XML file and hence no new API is needed. > > As simple discovery mechanism can be added to libvirt as follows: I agree with Dave that we need more information on the "big picture" of what you are trying to achieve overall. Just adding a <s3/> or <s4/> element on their own doesn't really seem useful to me, so I imagine you must have more extensive plans not yet described ?